Marois was using Wednesday to get ready for the debate and had no immediate response to Couillard.

Instead, one of her candidates leapt to her defence, saying Couillard's remarks are "not worthy of a party leader who aspires to be premier."

"This is an attempt at intimidation," said Agnes Maltais. "It's a threat directed at a premier."

The stakes are high as a large segment of Quebecers gets ready to watch the two-hour debate on Radio-Canada and provincial public broadcaster Tele-Quebec, beginning at 8 p.m. eastern.

Although Marois initially said she would only do one French-language debate -- and none in English -- all the leaders will also get together again next Thursday on TVA, the private network owned by star PQ candidate Pierre Karl Peladeau.

Couillard isn't fazed by being the rookie among the leaders, who will also include the Coalition's Francois Legault and Francoise David of Quebec solidaire.

"I've been preparing for the debate for a year-and-a-half," he said, referring to his year as Liberal leader and the six months that preceded his victory.

Couillard said during a swing through the Quebec City area he already knows the issues well from hashing them out with people during tours of the province.

"I'll go there and do my best. For me, it's the first time. I'll be there with veterans."

Legault acknowledges the debate is crucial for his party, which polls suggest is bleeding support.

"Usually one-third of the population decides after the debate for who they'll vote so nothing is decided yet," he told reporters in Montreal before settling down to prepare.

Legault said his main goal will be to remind voters about his party's message -- no sovereignty referendum and a focus on the economy. He also wants to see if Couillard's confidence is justified, given his "Philippeflops" on issues.

"I want to test him to see if he did his homework, to see if he's ready to govern Quebec because I've seen in the last few months that this guy is not ready to govern."

Despite the fireworks so far in the campaign leading up to the April 7 election, analysts say the debates are often when people really start paying attention to what the parties are saying.

"It is a key moment, an important moment," said Martin Papillon, a political scientist at the University of Ottawa.

"It's a moment for parties to set the agenda for the next few days or for the last part of the campaign and it's a moment also for leaders to establish a direct connection with the people."

Andre Juneau, a political scientist at Queen's University in Kingston, Ont., noted the debates can also help parties bolster their troops, citing the after-effects of then-Liberal leader Jean Charest's 2003 performance against Bernard Landry, who led the PQ.

"He did very well," Juneau said. "He surprised his troops, who were becoming a bit discouraged, and this had a major impact on the energy of the campaign. Indirectly, it had an effect on voters."

Charest won that election.

Papillon and Juneau agreed Couillard will be a major target in the debate because of his party's momentum. Marois is also likely to try to change the campaign's emphasis, which has been on the possibility of an unpopular sovereignty referendum, they said.

"It's clearly her campaign to lose," said Papillon. "So far things are OK but if she doesn't readjust in the next two weeks, the winds of change are going to be really too strong.

"This week and the next week are really the key weeks of the campaign so Madame Marois really has to shift the focus. I wouldn't be surprised if we see more of a negative campaign from the PQ from now on, more aggressive, more personalized toward Couillard."

Papillon said he doubts Couillard will be able to focus as much as he would like on sovereignty in the debate because of the format. He added the Liberal leader also will want to show his range on other topics.

Juneau, on the other hand, said sovereignty talk will likely be inescapable.

"That's what they'll be pushing each other to talk about, exploiting their respective weaknesses."

And what about the fabled knockout punch?

"I'm attracted by the Super Bowl or the World Series because of the drama, the risk of mistakes, the chance there will be some heroic gesture," said Juneau. "That's why some people like debates, I think.